Due to the growing demand for speed and capacity of telecommunication systems, high-bit rate optical fiber networks are needed in order to provide sufficient capacity for data transmission. As electronic circuitry is used for processing data which have been transferred by optical fiber networks previously, photodiodes are needed in order to convert an optical signal to an electric signal at the end of an optical fiber.
Usually, photodiodes used in optical communication networks are of the p-i-n-type. When converting an optical signal to an electronic signal, the optical power provided is absorbed by an absorption layer of the photodiode made from intrinsic semiconductor material, thereby generating pairs of electrons and holes. By providing an electric field inside the intrinsic absorption layer by means of the adjacent p- and n-contact layers, the charge carriers drift to the respective p- and n-contact layers, thereby generating an electric signal proportional to the optical signal provided. The time needed to generate the electric signal is given by the drift velocity and the drift length of the charge carriers and the time needed to reestablish the electric field given by the capacity of the photodiode and the resistance of the photodiode and its dedicated electrical signal lines. Therefore, a thin absorption layer would be preferred in order to minimize the drift length and a thick absorption layer is favorable by minimizing the capacity. Furthermore, a thin absorption layer can provide only a small volume and therefore a low quantum efficiency for charge carrier generation.
It is therefore an object of the present invention to provide a high-speed photodiode and a photodetector based on these photodiodes which can be used at frequency above 40 GHz.